In-Liquid Plasma Modified Nickel Foam: NiOOH/NiFeOOH Active Site Multiplication for Electrocatalytic Alcohol, Aldehyde, and Water Oxidation

Abstract

The oxygen evolution reaction (OER) and the value-added oxidation of renewable organic substrates are critical to supply electrons and protons for the synthesis of sustainable fuels. To meet industrial requirements, new methods for a simple, fast, environmental-friendly and cheap synthesis of robust, self-supported and high surface area electrodes are required. Herein, a novel in-liquid plasma (plasma electrolysis) approach for the growth of hierarchical nanostructures on nickel foam is reported on. Under morphology retention, iron can be doped into this high surface area electrode. For the oxidation of 5-(hydroxymethyl)furfural and benzyl alcohol, the iron-free, plasma-treated electrode is more suitable reaching current densities up to 800 mA cm−2 with Faradaic efficiencies above 95%. For the OER, the iron-doped nickel foam electrode reaches the industrially relevant current density of 500 mA cm−2 at 1.473 ± 0.013 VRHE (60 °C) and shows no activity decrease over 140 h. The different effects of iron doping are rationalized using methanol probing and in situ Raman spectroscopy. Furthermore, the intrinsic activity is separated from the number of active sites, and, for the organic oxidation reactions, diffusion limitations are revealed. The authors anticipate that the plasma modified nickel foam will be suitable for various (electro)catalytic processes.